scripts: sphinx-pre-install: run on a supported version

The scripts/sphinx-pre-install is used to detect problems at
the system environment and adjust it to build the Kernel
documentation. If the version is too old, it won't run, though.

Check if the version which started the script is valid. If not,
seek for a new one that is compatible with documentation
build.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/76627055a7f82f6a79296ddbd873fa5ac8f82a1d.1754992972.git.mchehab+huawei@kernel.org

scripts/sphinx-pre-install.py

@@ -5,6 +5,9 @@
 # pylint: disable=C0103,C0114,C0115,C0116,C0301
 # pylint: disable=R0902,R0904,R0912,R0915,R1705,R1710,E1121
 
+# Note: this script requires at least Python 3.6 to run.
+# Don't add changes not compatible with it, it is meant to report
+# incompatible python versions.
 
 import argparse
 import os
@@ -16,7 +19,6 @@ from glob import glob
 
 def parse_version(version):
     """Convert a major.minor.patch version into a tuple"""
-#
     return tuple(int(x) for x in version.split("."))
 
 
@@ -27,6 +29,7 @@ def ver_str(version):
 
 
 RECOMMENDED_VERSION = parse_version("3.4.3")
+MIN_PYTHON_VERSION = parse_version("3.7")
 
 
 class SphinxDependencyChecker:
@@ -132,6 +135,65 @@ class SphinxDependencyChecker:
         # Python not found at the PATH
         return python_names[-1]
 
+    @staticmethod
+    def get_python_version(cmd):
+
+        result = SphinxDependencyChecker.run([cmd, "--version"],
+                                            capture_output=True, text=True)
+        version = result.stdout.strip()
+
+        match = re.search(r"(\d+\.\d+\.\d+)", version)
+        if match:
+            return parse_version(match.group(1))
+
+        print(f"Can't parse version {version}")
+        return (0, 0, 0)
+
+    @staticmethod
+    def find_python():
+
+        patterns = [
+            "python3.[0-9]",
+            "python3.[0-9][0-9]",
+        ]
+
+        new_python_cmd = None
+
+        # Seek for a python binary newer than MIN_PYTHON_VERSION
+        for path in os.getenv("PATH", "").split(":"):
+            for pattern in patterns:
+                for cmd in glob(os.path.join(path, pattern)):
+                    if os.path.isfile(cmd) and os.access(cmd, os.X_OK):
+                        version = SphinxDependencyChecker.get_python_version(cmd)
+                        if version >= MIN_PYTHON_VERSION:
+                            return(cmd)
+
+    @staticmethod
+    def check_python():
+
+        cur_ver = sys.version_info[:3]
+        if cur_ver >= MIN_PYTHON_VERSION:
+            return
+
+        python_ver = ver_str(cur_ver)
+
+        new_python_cmd = SphinxDependencyChecker.find_python()
+        if not new_python_cmd:
+            print(f"ERROR: Python version {python_ver} is not spported anymore")
+            print(f"       Can't find a new version. This script may fail")
+            return
+
+        # Restart script using the newer version
+        script_path = os.path.abspath(sys.argv[0])
+        args = [new_python_cmd, script_path] + sys.argv[1:]
+
+        print(f"Python {python_ver} not supported. Changing to {new_python_cmd}")
+
+        try:
+            os.execv(new_python_cmd, args)
+        except OSError as e:
+            sys.exit(f"Failed to restart with {new_python_cmd}: {e}")
+
     @staticmethod
     def run(*args, **kwargs):
         """Excecute a command, hiding its output by default"""
@@ -1107,6 +1169,7 @@ def main():
 
     checker = SphinxDependencyChecker(args)
 
+    checker.check_python()
     checker.check_needs()